For the vertical or planar electronic power device (MOS components, bipolar transistors, J-FET, MISFET, Schottky or PIN diodes, thyristors), optoelectronic component (Laser, LED) and photovoltaic component (solar cells) market, it is interesting to utilize an AlxInyGa(1-x-y)N (x between or equal to 0 and 1, y between or equal to 0 and 1, x+y less than or equal to 1) conducting substrate and preferably a bulk GaN (or “freestanding”) substrate.
These substrates are, however, difficult to manufacture with current technologies and remain very expensive.
A proposed alternative consists of a heterostructure comprising a thick active layer of AlxInyGa(1-x-y)N (preferably in doped GaN) formed on a conductive substrate.
But the growth of thick layers with a good crystalline quality is still difficult with current methods if the seed substrate is not of the same material as the material epitaxied.
The epitaxy of a thick layer of GaN (approximately 10 micrometers) on a seed substrate such as doped Si or SiC, due to the differences in the coefficient of thermal expansion (CTE) and lattice parameter between the materials, leads to the formation of defects and cracks in the layer which reduces the effectiveness of the electronic, optical or optoelectronic devices formed on this material.
In addition, as document WO 01/95380 discloses, this epitaxy necessitates the utilization of a buffer layer—for example a layer of AlN—between the seed substrate and the GaN that presents high electric resistance.
The epitaxy of a thick layer of GaN on a sapphire substrate followed by the transfer of the layer to a conductive substrate by laser detachment is an expensive process.
In addition, the choice of these materials does not allow a dislocation density of less than 107 cm−2 to be reached in the active layer.
In addition, the layer thus formed presents very significant bending which necessitates long preparation steps (polishing, etc.) so that it may be bonded and transferred to a final substrate.
In addition, the transfer of a layer of GaN from a bulk substrate by the SMARTCUT® technology does not enable the desired thicknesses to be reached in a satisfactory manner to date.
Document US 2008/0169483 describes the formation of an epitaxy substrate comprising a seed layer of GaN transferred by the SMARTCUT® technology to a support substrate.
A layer of conductive GaN is then deposited on the seed layer and then it is transferred to a thermally and electrically conductive support.
This method is complex since it involves two transfers of the active layer of GaN to form the final conductive structure.
Document US 2009/278233 describes the formation of a heterostructure for light-emitting devices.
The manufacturing of the heterostructure comprises first a step of providing on a handle substrate a seed layer suited for the epitaxial growth of an active layer made of a III/N material and a step of growing the active layer on the seed layer, thus producing an intermediate structure.
This intermediate structure is then bonded to a final substrate, preferably via a eutectic bonding layer, and the handle substrate is removed.
This method is thus complex since it involves the use of two different support substrates, the first one for the epitaxial growth of the active layer, the second one for the operation of the component.
Therefore one seeks to design a heterostructure for electronic power components, optoelectronic components or photovoltaic components and a method of manufacturing the heterostructure in view of obtaining a thick, crack-free monocrystalline layer of a material of composition AlxInyGa(1-x-y)N on a support substrate, not presenting the disadvantages of methods from the prior art. In particular, a simplification of the process steps is sought.
More precisely, the heterostructure must present the following properties:                a thick active layer, i.e., with a thickness greater than or equal to 3 micrometers, preferably greater than 10 micrometers,        a good vertical electrical conductivity despite interfaces between different materials forming the heterostructure, i.e., a total electrical resistivity of less than or equal to 10−2 ohm·cm,        a low electrical resistivity of the support substrate, i.e., typically lower than 10−3 ohm·cm,        a high thermal conductivity of the heterostructure, i.e., typically greater than or equal to 100 W/m·K,        a low dislocation density in the active layer, i.e., of less than or equal to 107 cm−2.        
In the case of electronic power components, the active layer of the heterostructure shall comprise a main portion with a thickness representing between 70 and 100% of the thickness of the active layer, the main portion being weakly doped so as to enable a dispersion of the electric field over the thickness of the active layer.
In the present text, “layer portion” is understood to refer to a part of a layer considered in the sense of the thickness of the layer. Thus, a layer may be constituted of several stacked portions, the sum of the thicknesses of portions being equal to the total thickness of the layer. The different portions of the active layer may be in the same material, but with different doping, or rather may be in different materials of composition AlxInyGa(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
Thus, the active layer of a PIN diode may be designed with alternating InGaN/GaN/InGaN or doped p GaN/weakly doped GaN/doped n GaN layers.
The active layer for optoelectronic or photovoltaic components may be constituted of a stack of layers in different materials of composition AlxInyGa(1-x-y)N, where 0≦x≦1, 0≦y≦1 and x+y≦1.
In addition, “subjacent” designates a layer portion the farthest removed from the surface of the heterostructure and “superjacent” designates a layer portion closest to the surface of the heterostructure. By way of example, the active layer of a PIN diode comprises a single subjacent and superjacent layer on both sides of the main portion.
Another object of the invention is to design a support adapted for epitaxy of the active layer in view of forming the heterostructure described above.
More precisely, this epitaxy support must enable growth of the thick active layer without forming cracks and must in addition present electric properties compatible with the intended applications.